While I haven't dealt with that fetish before, I believe it falls into the category of something that was done to her by another young man and she liked it so much that she's decided that that is the only way she's going to get off.

This works because, in most instances, a woman can always find some man to cater to her wants, no matter how inconvenient, as long as the possibility of sex is there.

So, first, I would point out that she's forcing you to do something that reminds her of some other guy.

Second, none of this is a problem, even without those, I'm almost positive she has the same "pleasure" points as other girls. If you have good sex together, along with the months both of you have invested in whatever relationship you have, eventually she will reach a point where she is willing to compromise and you don't have to do it EVERYtime.

Until then, slowly put her in positions where she doesn't have time to think of those chocolatey treats. Two that come to mind are quickies in unusual places and, after having her stay over, catch her as she's starting to stir...warm her up by kissing her neck/ back (this should also reveal your intentions) and slide in to home base.